Absorption heating and cooling system



United States Patent [72] Inventor Louis 11. Leonard, Jr.

Dewitt, New York [21] Appl. No. 784,617

[22] Filed Dec. 18, 1968 [45] Patented Oct. 27, 1970 [73] AssigneeCarrier Corporation Syracuse, New York a corporation of Delaware [54]ABSORPTION HEATING AND COOLING SYSTEM 9 Claims, 1 Drawing Fig.

521 0.5. CI 165/2, 62/114 [51] Int. Cl F25b 29/00 [50] Field of Search62/1 14,

[56] References Cited UNITED STATES PATENTS 3,153,441 10/1964 Pippert etal. 165/62X Primary Examiner-William E. Wayner Attorneys--Harry G.Martin, Jr. and J. RaymOnd Gurtin ABSTRACT: A heating and cooling systemutilizing an absorption refrigeration system including a generator, acondenser, an absorber, and an evaporator, when operating in the coolingmode. Heating passage means is provided for converting the system to aheating mode operation by mixing the absorbent solution and refrigerantto form a heating medium, passing the heating medium through thegenerator for heating, and passing the heated heating medium through aheat exchanger to provide heat to a desired location. Variousliquid-filled vapor traps are established when operating in the heatingmode by accumulation of the heating medium. A layer of a suitableadditive, preferably having heat transfer promoting properties in thecooling mode, such as 2-ethyl-n-hexanol, is formed over the surface ofthe heating medium at locations exposed to low ambient temperatures toinhibit evaporation of the heating medium.

ABSORPTION HEATING AND COOLING SYSTEM BACKGROUND OF THE INVENTIONHeating and cooling systems are known which utilize an absorptionrefrigeration cooling mode of operation and a condensation heating modeof operation. These systems have a number of disadvantages relating tothe heating mode condensation process and the possibility of freezing orsolidification of the refrigerant and absorbent solution when the systemis located in a low ambient temperature environment. These problems areovercome by the heating and cooling system described in my applicationSer. No. 784,724, filed Dec. 18, I968 filed concurrently herewith. Thesystem described in that application employs a heating medium comprisinga mixture of absorbent solution and refrigerant having excellentantifreeze properties which is heated in the generator and passedthrough a suitable heat exchanger to provide heat to a desired location.

When switching a system of the type described from the heating to thecooling mode of operation, it is desirable to form certain liquid-filledvapor traps in the system which are exposed to condenser or absorbertemperature. A problem arises if it is desired to heat the liquidheating medium to a temperature corresponding to a vapor pressure whichis higher than the vapor pressure existing in the absorber andcondenser, because of the tendency of the heating medium to boil. Thiscan be partially overcome by forming certain specially designed trapshaving a cold leg containing heating medium which remains cool and outof circulation in the system. However, still further protection may bedesirable against the possibility of vaporizing or boiling refrigerantfrom the heating medium during operation at very low ambient condenserand absorber temperatures.

SUMMARY OF THE INVENTION In accordance with this invention, there isprovided a heating and cooling system utilizing an absorptionrefrigeration cooling mode of operation. Heating passages are providedto switch from cooling to heating operation by mixing absorbent solutionand refrigerant to form a heating medium. The heating medium is heatedin a generator and circulated through a suitable heat exchanger toprovide heat to a desired location from which the heating medium isreturned to the generator for reheating. Liquid traps preventing thepassage of vapor are formed at certain locations in the system whenoperating in the heating mode. For example, it is preferred to form aliquid trap in the refrigerant vapor passage between the generator andthe condenser when operating in the heating mode.

In order to prevent evaporation of refrigerant or boiling of the liquidheating medium during heating operation, an excess quantity of asuitable additive, which is immiscible with the heating medium and has alower specific gravity than the heating medium, is introduced into thesystem and passed to the locations at which the traps are formed. Apreferred liquid additive is one such as Z-ethyI-n-hexanol, which alsoimproves heat transfer in the cooling mode of operation. The immiscibleliquid additive gravitationally separates from the liquid heating mediumand forms a layer on the surface of the liquid heating medium ofsufficient thickness to substantially inhibit the diffusion ofrefrigerant molecules therethrough. Consequently, the heating medium maybe safely heated to a temperature corresponding to a vapor pressure,which exceeds the pressure in the condenser and absorber, withoutresulting in boiling or vaporization of the absorbent from the heatingmedium.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematicillustration, partly in cross section, of a heating and cooling systemin accordance with this invention illustrating certain liquid levels asthey are present in the heating mode of operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT This invention will be describedwith respect to a preferred embodiment wherein a two-stage adiabaticrefrigerant evaporator and a two-stage air-cooled absorber are employed.However, this invention may be employed in systems having any number ofeither adiabatic or nonadiabatic evaporator stages.

The preferred refrigerant is water and the preferred absorbent is anaqueous solution of lithium bromide, although otherabsorbent-refrigerant combinations, especially those including a lithiumhalide salt, may be employed instead. Asused herein, a concentratedsolution of lithium bromide which is strong in absorbing power will bereferred to as strong solution and a dilute solution of lithium bromidewhich is weak in absorbing power will be referred to as weak" solution.Refrigerant"as used herein includes pure water, which may be referred toas concentrated refrigerant, and water having lithium bromide therein,which may be referred to as dilute refrigerant. An additive, such as2-ethyl-n-hexanol, is added to the absorbent solution.

Referring to the drawing, the system comprises a generator 10, acondenser 11, an absorber 12 having a low-pressure stage 13 and ahigh-pressure stage 14, and adiabatic evaporator15 having alow-temperature stage 16 and a high-temperature stage 17, an airconditioning heat exchanger 18 and a solution heat exchanger 19. Heatexchanger 18 provides sensible heat exchange between cold liquidrefrigerant and air being conditioned when the system is connected toprovide refrigeration. In such operation, heat exchanger 18 functions asa heat absorbing heat exchanger.

Generator 10 comprises a shell 22 having a plurality of fire tubes 23extending therethrough. Fuel burner 24 discharges hot gas through firetubes 23 into flue gas collector 25. Other types of generators, such asthose employing steam or hot water as a heating fluid, may bealternatively utilized.

Weak absorbent solution is supplied to generator 10 and boiled thereinto concentrate the solution in the cooling mode of operation. Theresulting strong absorbent solution passes through strong solutionpassage 28 and the shell side of solution heat exchanger 19 to strongsolution pump 29. The strong solution is pumped through strong solutionpassage 30 to lowpressure vapor header 33 disposed at the top oflow-pressure absorber stage 13.

Low-pressure absorber stage 13 comprises a plurality of verticallydisposed finned absorber heat exchange tubes 34 connected at their upperends by a low-pressure vapor header 33 and at their lower ends by alow-pressure liquid header 35. Strong solution overflows the open upperends of absorber tubes 34 and passes downwardly along the interiorsurface of the absorber tubes while absorbing refrigerant vapor therein.The heat of the absorption process is rejected to ambient air passedover the exterior surfaces of absorber tubes 34 by fan 36. The absorbentsolution is somewhat diluted by absorption of refrigerant vapor in tubes34, so that the solution collected in low-pressure liquid header 35 isof intermediate concentration. The intermediate solution passes throughsiphon tube 37 having an upwardly arched portion 38 into high-pressurevapor header 42 of high-pressure absorber stage 14.

High-pressure absorber stage 14 comprises a plurality of finned verticalabsorber heat exchange tubes 43 joined at their upper ends byhigh-pressure vapor header 42 and at their lower ends by high-pressureliquid header 44. Intermediate absorbent solution overflows the upperopen ends of absorber tubes 43 and passes downwardly along the interiorsurfaces of the absorber tubes while refrigerant vapor is being absorbedtherein. The heat of the absorption process is rejected fromhigh-temperature absorber stage 14 to ambient air passed over pressureliquid header 44 is weak in absorbing power. The weak solution passesfrom the low-pressure liquid header 44 through a siphon tube 46 havingan upwardly arched portion 47through weak solution passage 51 into weaksolution sump 52. The weak solution then passes from weak solution sump52- through weak solution passage 53 to weak solution pump 54. The weaksolution is thenupumpedthrough weak solution passage 55 and the interiortubes of solution heat exchanger l9through an upwardly extending loop56, and weak solution passage 57 into generatorlo for reconcentration.

f "Refrigerant vapor is formed in generator,10 by the boiling ofabsorbent solution. This refrigerant-vapor passes'fromt vapor pressureof refrigerant and absorbent solution in the system-undervariousoperating conditions as explained in Leonard application Ser. No.784,725, filed Dec. l8, 1968 ,tr ol valve 107 is disposed .inpassagef105which communicates r A heating passage 105 communicates withpassage 95 at a pointbelow the top of upwardly arched loop 96. A nodecon- 7 at its otherend with generator through passage 57.

generator 10" to condenser '11 through refrigerant vapor passage 60.Refrigerant vapor passage 60 hasan upwardly extending loop 61 and adownwardly extending loop or trap 62 therein, which are free of liquidin the cooling'mode. 'A.-vent line 63 vents the upper portionQof loop 56to thecondenser pressure in passage 60.; v r

Refrigerant condenser 11 comprises a plurality of vertical 11 passesfrom header 67through condensatepassage 68having a downwardly extendingloop or trap 69 into high temperature evaporator stage 17, of adiabaticrefrigerant evaporator High-temperature.evaporator stage 17 comprises ashell 74' havingpacking material 75 therein. A vapor passage 76 extendsbetween high-temperature evaporator stagef lo7 and vapor header 42 ofhigh-pressure absorber stage 14; A smallquantity of refrigerantisevaporated from refrigerant passing 1 Another heating passage 110having a mode control valve 1 11 therein communicates betweendisehargeof ,s olutionpassage 30 and absorbent sump 52. A third heating passage115, which comprises a generator effluent passage, has an upper end con-"nected between upwardly arched portion 61 and downwardly arched portion62 of passage Effluent passage 115 has a .downwardly extendingloop 116and an upwardly extending loop 117' thereinThedownward leg 118 ofupwardly extending'loop 117 is connected to refrigerant sump 85 and isof I finned tubes'66 connected at their upper ends byrefrrgerant largerdiameter than the legs of loop 116 to prevent siphoning of loop 116. 2 g

When the system is in the cooling mode of operation, mode control valves107 and 111 are closed. Loop 116 is filled with sufficient; liquid tobalance the pressuredifi'erence between generator 10 and refrigerantsump 85 to prevent passage. of vapor therebetween. At or above designambient absorber temperature, the refrigerant circulated throughevaporator 15 and heat exchanger 18 is preferably substantially purewater and the strong absorbentsolution concentration is preferablythrough evaporator stage 17, thereby flash-cooling the r.

remaining refrigerant. Thecooled refrigerant passeslfrom Vhigh-temperature evaporator stage 17 to low-temperature evaporator stage16 through refrigerant passage 78-having a downwardly extending trap 79.

Low-temperature evaporator stage 16 comprisesa shell 80 1 having packingmaterial 81 therein and a refrigerant vapor passage 82 communicatingwith vapor header 33'0f low-pressure absorber l3.,As in the precedingstage, a small quantity of refrigerant is evaporated in low-temperatureevaporator'stage V 16' which results in flash-cooling the remainder ofrefrigerant passing therethrough. In all, only about 1 percent of thetotal heat absorbing heat exchanger 18 included therein may bealternatively employed. e The cold refrigerant then passes fromlow-temperature evaporator stage 16 through refrigerant passage 84 intorefrigerant sump 85. The cold refrigerant passes from sump 85 throughrefrigerant passage 86 to. pump 87 and is pumped through passage 88 to.inlet header: 90 of heat absorbing heat through the fan-coilunit'located induct 93. Heat exchanger 18 passes cold liquid refrigerantin heat exchange relation with 1 about 64.5 percent lithium bromide byweight.

To switch from the cooling mode of operation to the heating mode,control valves I07 and 111 are opened. Operation of pumps 54 and 29, andfans 36 and 45 is discontinued. Opening of valve 107 causes the fluidpassing through passage 95 from heat exchanger 18 to be diverted intopassage 105 because passage 105 and connecting passage 57 is below. thetop of loop 96 which is above the top of loop 61. Gnerator 10 and loops61 and 62 are flooded with a mixture of refrigerant and absorbentsolution by pump 87. The'liquid level in passage is below the junctionof vent line 63 and below the top of loop 96 as shown in the drawing.All of therefrigerant and-absorbent solution in the system is mixedtogether to form a heating solution when the system is in the heatingmode.

A major portion of the heated solution (90 percent) passes upwardlythrough loop 61 into passage 115. The level of the heated solution isabove the level of upwardly, extending loop 117 and it will flow bygravity through pass age 115 through downwardly extending leg 118 intorefrigerant sump 85. The heated solution passes from refrigerantsump 85through the heat exchanger 18.A minor portion (l0 percent) of thesolugtion heatedin generator 10 continuesto pass downwardly throughpassage 28, the shell side of. heat exchanger 19, through inoperativepump 29, passages30 and 110, into absorbent sump 52,and through controlpassage 100 into refrigerant sump 85, from which itpasses-to heatexchanger 18, as previously described.

Whenit isdesired to terminate heating and return to the cooling mode ofoperation, mode control valves 107 andlll are closed. Pumps 54 and 29andfans-36and 45 are again energized. Closing of valve 107 terminatesdirect flow of solution from heat exchanger 18 to generator10..lnstead,solution is pumped from heat exchanger18, through upwardly extendingloop 96 and passage 95,'and serially through high temperature evaporator.17 and low temperature evaporator 16 of the air passing thereover tocool the air which constitutes a refrigeration load in the cooling modeof operation. After absorbingheat from theair being cooled, the warmedliquid refrigerantpasses through refrigerant passage. having an 7 1";upwardly extending loop 96 and restricted spray. nozzle 98 back tohigh-temperature evaporator. stage 17 of adiabatic evaporator 15 forrecooling of the refrigerant. Some I drawing. This passage serves toadjust the concentrationand longer passes solution. I I

. The volume of strong absorbentsolution passing to sump 52 willdecrease as refrigerant is boiled from it in the generator, and thelevel of solution in sump 52 willtend to drop. Converadiabaticevaporator.15. The solution in generator 10 is heated to the boiling temperatureto concentrate the solution. The level of solution in the generatordropsso that vapor passage 60 is free of liquid, and loop 116 is sealed butno sely, the quantity of refrigerant passing through evaporator 15 willincrease due to the refrigerant added to the refrigerant circuit fromcondenser 11, and the level of refrigerant in sump will tend to rise.When the head of refrigerant in sump 85 tends to exceed the head ofabsorbent solution in sump 52, diluted refrigerant will flow throughrefrigerant reconcentration and vapor pressure control line 100 intoabsorbent sump 52 to balance the liquid heads in the two sumps. Atabsorber ambient temperature above design conditions, dilutedrefrigerant will continue to be bled from sump 85 into sump 52 until therefrigerant has been substantially concentrated and the absorbentsolution has been concentrated to the desired full-load design operatingconcentration.

If the temperature of air passed over absorber 12 is less than thedesign temperature, the process of concentrating the absorbent solutionand the refrigerant will stop at some intermediate concentration wherean equilibrium is reached between absorber capacity and refrigerationdemand. From then on, the concentration of absorbent and refrigerantwill adjust itself to provide a variable pressure effect which justbalances refrigeration load against absorber capacity.

Trap 62 is filled with liquid during heating mode of operation byopening of valves 107 and 110. The condenser side leg of solution intrap 62 may have a higher vertical elevation than the generator side legdue to a difference in pressures between the condenser and the generatorwhen the condenser is exposed to relatively low ambient temperatures. ltwill be noted that the generator effluent passage which includesupwardly arched loop 61 and heating passage 115 is connected to thegenerator side leg and is remote from trap 62 in the sense that liquidin the condenser side leg of the trap does not circulate through heatingpassage 115 to any substantial extent. This feature assures a quietrelatively cool leg of solution in the condenser side of the trap whichis effective to prevent direct vapor communication between the generatorand the condenser.

In accordance with this invention, a layer 121 of a liquid additive isformed on the surface 120 of the heating medium in the condenser sideleg of trap 62. Additive 121 may comprise any material having arelatively low volatility, a specific gravity less than that of theheating medium in trap 62, and which is relatively immiscible with theheating medium. Liquid additive 121 is preferably a material throughwhich refrigerant molecules diffuse relatively slowly so that thematerial will substantially prevent vaporization or boiling ofrefrigerant from the heating medium in trap 62, even though thetemperature of the heating medium may provide a refrigerant vaporpressure higher than the pressure existing in condenser 11. Layer 121should have a sufficient thickness to effectively reduce the passage ofrefrigerant therethrough to an extent that the condensation ofrefrigerant in condenser 11 is of an unsubstantial amount.

Additive 121 is preferably also a material, such as Z-ethyl-nhexanol,which assists heat transfer when circulated through the absorber incontact with absorbent solution and refrigerant vapor, when the systemis operating in the cooling mode. However, various other materials maybe used to provide the required vaporization inhibiting function on theheating mode, such as an immiscible, low specific gravity, low vaporpressure silicon oil.

Any convenient means may be employed'for passingthe liquid additive tothe cold leg of trap 62. It is preferred to charge the refrigerationsystem with an excess quantity of 2- ethyl-n-hexanol over that amounteffective to produce increased cooling mode heat transfer and tomaintain the additive emulsified with absorbent solution and/orrefrigerant by the action of the various pumps in the system. The use ofcentrifugal liquid pumps is desirable for emulsifying the additive withother system liquids. Upon switching in the system from the cooling modeto the heating mode of operation, the heating medium will containsufficient emulsified additive so that layer 121 will settle out andoverlay surface 120 during operation of the system in the cooling mode.

In addition to liquid-filled vapor trap 62, there are other locations inthe system at which it is desirable to provide an additive layer on thesurface of the liquid in order to reduce the amount of vaporizationwhich can take place and to prevent freezing of the condensed vapor atlocations which might cause injury to the system. For example, trap 68is filled with refrigerant condensate which may be diluted withabsorbent during heating mode operation. It is desirable that a layer ofliquid additive 126 be formed so as to overlie the surface of the liquidin trap 68 during heating mode operation. Likewise, there are otherlocations in the system exposed to low pressure where vapor is preventedfrom passing which may be broadly referred to as traps, at which liquidlevels are formed when the system is in the heating mode. A layer ofalcohol 129 is preferably formed on the surface 128 of the liquid inweak solution passage 51. Layer 123 of additive preferably overliessurface 122 of liquid in refrigerant passage 184. Similarly, a layer 131of additive preferably overlies surface 130 of the liquid in weaksolution passage 55 when the system is operating in the heating mode.

The exact thickness of the additive layer may be empirically determinedfor a given system. It is preferred, however, that the thickness be inexcess of about 1 inch or more of additive for a lithium bromide systemwherein water is the refrigerant and 2-ethyl-n-hexanol is the additive.This condition requires charging the system with an amount of additivewhich is substantially in excess of that which would normally berequired for cooling operation. For example, the 2-ethyl-n-hexanol inthe machine may be on the order of about 10 percent or more of the totalliquid in the system. For purposes of this invention, the term excessadditive" means that quantity of additive which is sufficient to form alayer of substantial thickness on the surface of vapor traps or otherlocations exposed to absorber or condenser pressure during heating modeoperation and which is effective to materially inhibit vaporization ofrefrigerant from the liquid at those locations.

By means of this invention, it is possible to heat the liquid heatingmedium in the generator to a temperature cor responding to a vaporpressure which is higher than the pres' sure existing in the condenserand absorber during conditions of low ambient temperature, without thedanger of refrigerant vaporizing and condensing at unwanted locations.By inhibiting vaporization of refrigerant, it will be apparent that apotential heat loss from the system is reduced. Even more important,however, is the fact that the temperature of the heating medium may bemaintained sufficiently high to provide effective winter heating withoutvaporizing refrigerant at low ambient condenser temperatures. Inaddition, the danger of bursting condenser tubes by freezing of watervapor therein is substantially reduced by the practice of this inventionbecause the quantity of water evaporated is reduced.

While a preferred embodiment of this invention has been illustrated anddescribed, it will be appreciated that the invention may be otherwiseembodied within the scope of the following claims.

lclaim:

l. A heating and cooling system having a cooling mode of operation and aheating mode of operation:

A. said system in the cooling mode of operation comprising a generatorfor concentrating weak absorbent solution by boiling the weak solutionand vaporizing refrigerant therefrom, a condenser for condensingrefrigerant vaporized in the generator, an evaporator for evaporatingrefrigerant condensed in the condenser to provide cooling, and anabsorber for absorbing refrigerant vapor formed in the evaporator intoabsorbent solution concentrated in the generator, said system includingrefrigerant vapor passage means extending from said generator to saidcondenser for passing refrigerant vapor from the generator to thecondenser for condensation therein; said system in the heating mode ofoperation comprising heating passage means including generator effluentpassage means for passing a heated liquid heating medium from thegenerator through a heat exchanger in heat exchange relation with aheating load, and passagemeans for returning the heating medium to thegenerator for reheating therein;

wherein the improvement comprises:

C. said system in the heating mode of operation having a. j

liquid trap therein, the liquid trap having a liquid in at least one legthereof exposed to a relatively lowertern I V n tion and vaporizingrefrigerant therefrom, a condenser for condensing refrigerantvaporformed in the generator, an'

, perature than the liquid inthe generator; and q D. the'liquid in saidtrap comprising a liquid additive having a lower specific gravity thansaid liquid heating mti l'lt m and beingrelatively immiscibletherewith-said liquid ad ditive forming a layerrof liquid at the surfaceof said one leg ofthe trap which isjexposed to said lower tempera-mture, said, liquid additive having-a lower volatilitythan said heatingmedium and being present in a quantity to form slayer of sufficientthickness toinhibit vaporization of liquid heating mediurn from said oneleg of said trap.:- 2. An 'absorptionrefrigeration system as defined inclaim 1: A. said liquid trap being disposed in the" refrigerant "vaporpassage for. preventing direct vapor communication between the generatorand the condenser when the trap is flooded with liquid during theheating mode of operation of the system,"said one'legofsaid trap beingexposed to condensertemperaturei J 1 B. passage means for floodingsaidliquid trap withliquid heating medium duringthe heating mode ofoperation of C. said generatorefi'lue'nt passage means being connected 7to said generator at a location remote from said liquid, trap so thatheatedliquid heating medium bypasses said g 7 6.,A method of operating aheating and cooling system wherein said system in the coolingmodecomprises a'generator for concentrating "absorbent solution by boilingthe soluiiiiaporator for providing coolingby. evaporating refrigerantcondensed in the condenser, and an absorber forjabsorbing {refrigerantvapor formed in the absorberinto absorbent solu- -"tiqn concentrated inthe generator, said system including a refrigerant'vapor passage forpassing refrigerantvapor from said generatorto said con'densenandwhereinsaid system in -the heating mode of operationicomprises heatingpassage means for passing a heated heating medium from the genera- .torthrough a heat exchangerin heat exchange relation'with a comprises thesteps of forming a liquid trap comprising one of theliquids in thesystem and forming a lower vapor pressure 1 liquid layer over thesurface of said one liquid in the trap by operating the system in theheating mode, said liquid additive passing'said one liquidand a liquidadditive to said trap when I having a lower vapor pressure and a lowerspecific gravity than said one liquid, said liquids gravitationallyseparating from each other and forming a layer of additive overlyingthesurface of the one liquid, said layer being formedof sufficient liquidtrap in pa ssing from said generator to said heat exchanger,'jsaidliquid additive overlying the surface of said one leg of saidtrap. 3. An absorption refrigeration system as definedin claim 1 7. Amethod of operating a heating and cooling system as defined in claim 6including passing a mixture of liquid heating medium and liquid additiveinto said region when switching to the heating mode of operation tosimultaneously form said 1 liquid trap and said lower vapor pressurelayer.

wherein said liquid :additive comprises a material thatpromotes heattransfer when said system is operating in the cooling mode, saidmaterial having a lower specific gravity than said heating medium.

' 4. An absorption refrigeration system as defined in claim 1 whereinthe liquid in said trap comprises liquid heating medium having a layerof theadditjve overlying the surface of the heating medium in said oneleg thereof. 5. An absorption refrigeration system as defined in claim 1comprises Z-ethyl-n-hexanol, the liquid in said trap comprising whereinthe absorbent comprises'an. aqueous solution oflithi- V um bromide, therefrigerant comprises water and said'additive an aqueous solution oflithium bromide having a layer. of 2- ethyl-n-hexanol overlying thesurface of the'solutionin said one leg.

8. A method of operating a heatingand, cooling system as defined inclaim 6 including the step of emulsifying the liquid additive andtheliquid heating medium by simultaneously pumping additive and heatingmedium through a liquid'pump, and passing the emulsified additivefandheating medium to said region to simultaneously. form said liquid trapand said lower vapor pressure layer by gravitational separation thereof.

9. A'method of operating ahe'atingfland cooling system as defined inclaim 6 wherein said additiveisa material which :improves heat transferin the cooling modeof operation, and

the method includes the step of circulating the additive through theabsorberzin contactwith absorbent solution and refrigerant vapor'in theabsorber when said system is operating in the cooling mode.

